The present invention relates to a heat exchanger comprising finned tubes with the fins oriented transverse to fluid flow. In particular, the heat exchanger is applied for the extermination of pests and molds using heated air, and more particularly to the use of an explosion-proof heat exchange apparatus for safely directing heated air into and within an envelope enclosing an explosion hazard.
Extermination of pests, such as insects, present in stored food products has been conducted by chemical and by heating systems.
Chemical Systems
Methyl bromide has been the chemical of choice by the world for over 60 years for the control of stored food product pests as it is effective and safe to use with all foods, yet is lethal to known stored product pests in substantially any stage of development including eggs, larvae, pupae and adults, and also to rodents. However, methyl bromide is also hazardous to handle, requiring specially trained applicators under strict guidelines established by individual countrys"" governing bodies.
As well as being hazardous to humans during handling and treatment, methyl bromide has also been identified as an ozone depleting substance and its use in the food industries is scheduled to be banned by Jan. 1, 2005. Treatment for import and export applications will be the only industry that will have the continued use of methyl bromide after 2005 and it will be used strictly for quarantine situations only. Production quotas for methyl bromide have already been cut repeatedly with further reductions anticipated. Further, the cost of methyl bromide has increased four fold and is expected to double if not triple again before the next production quota reduction planned for the year 2003.
The EPA and USDA have estimated the phase-out cost to be in the billions of US dollars. In Florida and California alone, their best estimates are in the $4.0 billion dollar range. These two states were used as estimates because of their considerable involvement in supplying fresh fruits and vegetables throughout the US and Canada.
Alternate fumigants currently on the market have drawbacks that do not make them a safe alternative both to personnel and equipment. Further, the process for the introduction of new chemicals is a costly undertaking usually only within the capability of the major chemical companies.
One such chemical alternative is called ECO2FUME, which is a fumigant gas containing phosphine (2.6%) in carbon dioxide, provided by BOC Gases, a division of The BOC Group, Inc. Murray Hill, N.J. In Applicant""s experience, this fumigant is most effective when coupled with a heating process and is associated with corrosion of most yellow metals, electrical components and machinery; and further can be explosive in certain atmospheric conditions and humidity levels. Accordingly, the use of ECO2-Fume must be monitored and carefully controlled.
In large facilities or plants where fumigation can be applied, there is a requirement that the entire plant cease production and be closed for about 3-4 days. Such closures are associated with lost production and lost opportunity totaling approximately $10,000 per hour and often over $700,000 per day in larger plants.
Heat Treatment
A known alternative to the expense and increasing restrictions for the use of methyl bromide, is the use of high heating loads. It has been scientifically established that heat will eradicate all forms of pests, rodents and molds. The level of heat that is required in eradicating insects, beetles and molds is well above the ambient temperatures and a safe and abundant supply source of produced heat and temperatures is required.
There is a significant cost advantage to the implementation of heat treatment methods. When heat is used, problem areas of the plant can be dealt with on a localized and individual basis, production can be carried out as normal, and therefore the cost savings to the organization are extremely attractive. If the problem area involves active equipment, the area in question can be scheduled for a shutdown with minimal disruption to the overall operation of the plant. Therefore, heat treatment provides additional savings over and above that saved by avoiding the costs of fumigation chemicals.
Complications to heat extermination processes arise in that typical environments found in the food and grain storage industry are classified as explosive hazards due to dusts and particulates which are substantially always present. Therefore, such areas are classified by the US National Electrical Code (NEC) as Class I (atmospheres having flammable gases and vapors) or Class II (dusts), Division 1 (normally hazardous) and 2 (not normally hazardous). In Class II, the various atmospheres are divided into Group E (containing combustible metal dusts), Group F (containing combustible carbonaceous dusts) and Group G (containing combustible dust not included in Group E or F, including flour, grain, wood, plastic and chemicals).
One specific example relating to the aforementioned explosive complications was observed by Applicant at an actual mill undergoing heat treatment using conventional heat-producing equipment. The mill was classified as Class II, both Division 1 and 2, Groups E, F and G. The heating process used was very dangerous and typical of many current applications of such treatments in that the heating equipment used was not appropriately rated or classified for the hazardous operation. In this particular example, a naked propane flame was used. Further, there have been accidental fires caused by the use of open flamed apparatus in heat treatment applications for the extermination of termites. For this reason, the insurance industry is particularly interested in safer extermination methodologies.
Standards governing areas classed as being an explosion hazard do not permit ignition sources to be placed within the envelope and further, connections to ignition sources, gas or electrical, are not permitted to penetrate the envelope; blow back immediately following shutdown of flame or electrical heaters can involve residual ignition sources, such as high temperature surfaces, and present a hazard. Further, direct application of steam or products of combustion, results in excess moisture which is often detrimental to the treated area and its contents.
Applicant is not aware of any heaters which are available to this industry that have the capability of supplying the high output temperature parameters required and which are portable, nor are there heaters available for use in areas which present combustion or explosion hazards.
Applicant provides a heat exchanger which produces a surprisingly high efficiency and which, in its preferred embodiment, is part of a system which is highly adaptable for application in heat treatment processes for pest and mold extermination. Advantages of the present invention include: use of heat not chemicals and flameless heating with application of hot fluids such as steam, the invention can be classified for use in explosion-proof environments (Class II, Div 1 and 2, Groups E, F and G). The efficient heat transfer arrangement enables efficient heating or cooling of process fluid flows. Facilities that benefit from heat treatment with explosion proof equipment include: grain mills (flour, oats, bran, corn, rice etc.), grain storage depots; warehousing depots; rail cars; ship holds; food preparation facilities and wood shipping pallets or other such dunnage. Further, molds are also a major source of concern in the stored grain industry and as a possible cause of sick building syndrome. The present invention can also be effective against mold. Safe, portable steam heaters that can deliver high heating output can play a major role in the control of molds. Heat has been identified as an alternative to chemicals in the process of eliminating molds.
Accordingly, in a broad aspect of the invention, an improved heat exchange apparatus is provided adapted for insertion into an air plenum or housing with a bore through which a first fluid flows from an inlet to an outlet and having an array of two or more heat exchange tubes located in the bore through which a second fluid flows, the improvement comprising:
one or more linearly extending sections of the heat exchange tubes extending substantially parallel to a direction of air flow through the bore of the housing, the bore of the housing being substantially unimpeded so that the first fluid passes along a length of the tubes; and
a plurality of spaced and circumferential fins formed along the two or more heat exchange tubes and extending substantially perpendicular to the direction of air flow through the bore of the housing, the first fluid flowing through the bore of the housing and transverse to the fins for discharge from the outlet of the housing.
In another aspect, the invention is a system for the exchange of heat between first and second fluids comprising a tubular housing having an axis and a bore, the bore having an inlet for the admission of the first fluid and an outlet for the discharge of the first fluid; a fluid mover in the inlet for moving the first fluid from the inlet to the outlet of the bore; the improved heat exchange apparatus of parallel tubes and perpendicular fins; and means for moving the second fluid through the tubes so that heat is transferred through the tubes and fins between the first and second fluids.
Orientation of the fins substantially perpendicular to the flow of air through the heat exchanger permits a greater residence time of the transferring fluid (usually hot) within the heater and thus a more effective transfer of heat between the transferring fluid flowing in the tubes and the fluid (usually cooler air) flowing between the tubes and fins.
In yet another aspect, the invention comprises a method for the extermination of pests within an envelope of air comprising the steps of minimizing openings in the envelope; heating ambient air within the envelope using a heat exchanger; discharging the heated air into the envelope; and sustaining the flow of heated air into the envelope so that the temperature of air in the envelope is sufficiently high to kill pests.